Not Applicable
Not Applicable
1. Field of Invention
This invention pertains to drill bits. More specifically, the present invention is directed to drill bit blades adapted to be received in a drill body, the drill bit blades and drill body being keyed or indexed to facilitate centering.
2. Description of the Related Art
It is well known that drill bits adapted to bore through rock for the installation of roof bolts or to drill and blast to allow material to be removed in mines and the like have a carbide blade mounted or brazed in a transverse slot at the distal end of a drill body such as an elongate hollow tubular body or the like. One drill body used in association with a conventional dust collection system has access ports positioned near the blade, and the ports communicate with the inner bore of the body. Another embodiment used in association with a conventional auger system, for example, defines a post for mounting. Such blades are adapted to drill holes having a diameter of one inch and larger into the strata in the roof of a mine or the like. A vacuum is drawn through the hollow drill body to draw cuttings removed by the blade through the ports, through the hollow shaft of the drill bit, and to a collection location remote from the drilling. Alternately, a water flushing system may be used in which pressurized water is forced through the drill body, and out through the ports to flush the cuttings out the mouth of the hole. Also, an auger system can be used to remove the cuttings or material.
To withstand the wear incurred as such drill bits bore through the strata or rock, the blades of such drill bits are typically made of tungsten carbide and have a hardness in the range of 89.0 to 91.0 on the Ra hardness scale. A relatively small increase in the hardness of the tungsten carbide of the blade will substantially extend the useful life of a drill bit and enable the drill bit to bore or drill through substantially more rock before it becomes unusably dull. For example, a first drill blade which is harder than a second blade by a hardness rating of 0.5 on the Ra hardness scale may be capable of drilling through 50 percent or more rock or strata such as salt, gypsum, etc., when compared to the second drill blade.
On the other hand, harder carbide blades are more brittle than softer tungsten carbide blades and tend to fracture as a result of the stresses upon the blade. It has been found that tungsten carbide blades typically fracture along the central longitudinal axis of the blade as a result of the thrust forces applied during the drilling.
A drill blade attached to a drill bit and used to bore a cylindrical hole is subjected to a number of forces. At the center of the drill blade, the thrust forces arising from the drill being forced into the hole are maximized. At the outer edges of the blade, strong shear forces are developed as the blade removes stone to extend the hole. The cutting edges of drill blades generally wear most noticeably at the outer ends rather than at their centers because the blade surface footage and the sheer forces are greater at the ends of the blade than at the center. To wit, speed is measured as the ratio of distance to time. The time to complete one rotation of the blade is the same at any distance from the center. The distance traveled through one rotation is measured by the circumference at the particular radius, which is measured by xcfx80r2. Because one factor of the circumference is the square of the radius, the speed of the blade at any point increases exponentially from the center (zero) to the outer limit. If the blade is not centered on the body of the drill bit, it will be subjected to uneven forces causing stress and breakage of the blade.
Various drill bit blades have been provided for various uses. Typical of the art are those devices disclosed in the following U.S. Patents:
Of these patents, the ""638 patent issued to Massa et al., discloses several embodiments of cutting inserts. One in particular, illustrated in FIGS. 20A and 20B therein, includes a bottom surface defining a saw tooth shaped notch. The notch as a generally vertical surface, perpendicular to the bottom surface, and an inclined surface. A portion of the bit body including the slot has a bottom surface defining a saw tooth shaped projection. The projection has a surface which is generally perpendicular to the bottom surface of the slot and an inclined surface. The configurations of the cutting insert notch and the bit body projection are complementary, thereby serving a means for fixing the position of the cutting insert relative to the bit body. Other similar embodiments are disclosed by Massa et al., as well. However, Massa et al., do not disclose a cutting bit that extends across the entire diameter of the bit body and therefore are not concerned with centering the cutting insert.
Sheerer et al., in the ""689 patent, disclose an insert for use in a rotary drill bit define two opposing portions, each having a leading face. The first and second portions of the insert are offset from the center such that the cutting edge on the first portion is linearly aligned with the cutting edge on the second portion, the cutting edges meeting at the center of the cutting insert. The drill bit body must define a slot having a configuration to complement the offset configuration of the insert. If the slot in the drill bit body is closely toleranced, then the insert will be centered.
In the ""478 patent, Schimke discloses a masonry drill having an elongated axial body with at least one discharge groove and a transverse slot located at one end with a hardened drill bit insert brazed within the slot. The hardened insert has projections extending outward from flat planar surfaces which hold the insert in proper orientation within the axial drill body so that it may be brazed into place subsequent to insertion into the drill body. More specifically, the cylindrical drill body defines a transverse slot having smooth channel side walls. The drill bit insert defines at least one rib member on either side thereof, the rib members being fabricated from hardened carbide material. The drill bit insert is pressed into slot using a press with force sufficient enough to insert the carbide insert fully into the slot and allow the rib members to engage the side walls. As the drill bit insert is pressed into the drill body slot, the rib members score the side walls when properly inserted. Scoring of the side wall faces ensures the snug fit of the drill bit insert into the slot so that the insert may be subsequently properly affixed thereto by thorough brazing. However, Schimke does not address centering of the drill bit insert.
Sollami et al., in their ""937 patent, disclose a drill bit and blade. The blade defines a vertical rib positioned axially along the centerline of at least one side of the blade. The body defines a slot adapted to retain the blade. To wit, the slot is provided with a centrally located vertical recess along at least one side of the slot, each recess being adapted to receive a rib of the blade when the blade is positioned in the slot. Each rib serves not only to assist in centering the bit, but also to strengthen the bit.
In the ""210 patent, Sollami discloses a drill blade for a drill bit intended to be used to bore holes in the roofs of mines is made of hardened tungsten carbide. The blade has two end sections, one on each side of a central section, and the end sections have a higher degree of hardness than the hardness of the central section. Also, the central portion of the blade is made thicker than the distance between the planar surfaces of the end portions thereof such that the blade has a central protrusion and will be self centered on a slot in the bit body having a recess adapted to receive the central protrusion. A central insert is also made of a softer grade of tungsten carbide. In one embodiment, illustrated in FIG. 11 of ""210 patent, the insert has opposing sides each defining an arcuate shaped protrusion such that the width of the insert is greater than the distance between the sides of the blade body. As in the ""937 patent, these protrusions assist in centering the blade in the drill bit body.
The ""464 patent issued to Ojanen discloses a mine tool roof bit insert having a leading face inclined at a constant angle of between zero to three degrees with respect to the axis of rotation. The tapered leading face on either side of the insert yields a decrease in thickness from the top of the insert to the bottom. While Ojanen teaches a tapered bit, there is no provision for centering the bit in the drill body.
The ""540 and ""715 patents issued to Peay et al., are directed toward rotary roof mine bits comprising a bit body and an insert mounted therein. A top surface of the insert comprises two top sections which intersect a respective main surface of the insert to define first and second non-linear cutting edge. As indicated, the preferred embodiment includes an axial notch disposed at a center of the top surface. It was disclosed by Peay et al., that it has been conventional to provide a roof bit insert with a center notch in lieu of a chisel edge in order to increase the penetration rate of the bit. Due to the low rotational speed as described above, a chisel edge does not perform a cutting action, but rather serves to grind or pulverize the center region of the hole being drilled. By providing a center notch in lieu of a chisel, a center core of rock material is formed, that core being more easily broken into fragments, thereby improving the penetration rate.
Another prior art device not disclosed in the aforementioned patents is illustrated in FIGS. 1 and 2. The illustrated prior art blade defines a rectangular extension on the leading end of each face of the blade. At the distal end of each cutting edge, a sharp corner is defined. In operation, such a configuration leads to premature failure of the blade as the point is disposed where the greatest rotational velocity is achieved.
The present invention is a roof bit blade insert for use in mining and other associated applications. The blade is configured to be readily centered within a drill body slot in order to equalize stress on each side of the blade during a drilling operation. Various embodiments of the blade of the present invention are provided.
Generally, the blade defines two opposing faces, each having a leading end and a trailing end. The top surface of the blade is generally sloped down from the leading end of one face to the trailing end of the opposing face to form a cutting edge. Further, the leading end of one face extends slightly beyond the trailing end of the opposing face in order to prevent the blade from binding during a cutting operation. The opposing faces are disposed either vertically or with a taper from a top edge to a bottom edge of the blade. Each embodiment of the blade of the present invention defines an indexed protrusion disposed at either or both of the leading and trailing ends of each face. A centered protrusion is defined on several embodiments.
The centered protrusion is provided to strengthen the mid-section of the blade, as well as to assist in centering the blade in a drill body slot. A relief is defined at the upper end of the centered protrusions. Each relief slopes inwardly so as to converge toward the center of the blade, thereby reducing the thickness of the blade in the immediate proximity of the center. The relief helps reduce stress at the center of the blade, thereby enabling better penetration through the rock strata and prolonging its useful life.
The indexed protrusions defined by the leading and trailing ends of the blade are defined by several configurations. In one embodiment, each of the leading end and trailing end protrusions defines an arcuate configuration. In a further embodiment, the leading end and trailing end protrusions are defined by a compound curve. In another embodiment, the leading end protrusions are defined by a butterfly taper, which is an outward taper from the center of the blade to the outer edge thereof. In an alternate to this embodiment, a curved relief surface transitioning from the leading end protrusion to the end of the blade is defined. In a still further embodiment, the leading end protrusions are defined by half-butterfly taper, or an outward taper from an approximate midpoint between the center of the blade and the outer edge of the blade to the outer edge of the blade. In an alternate to this embodiment, a curved relief surface transitioning from the leading end protrusion to the end of the blade is defined.
In several of the embodiment, the blade defines a notch at the center thereof. The center notch reduces stress created by grinding and allows rock to be more efficiently broken and removed. The notch is defined by a symmetrical geometric configuration such as circular, elliptical, rectangular, and combinations thereof. A curved transition from the notch to the cutting edge is provided to allow for grinding of the blade without immediately defining a point at the top of the cutting edge, thereby strengthening the transition and extending the life of the blade. A drill point is defined at the bottom of the center notch in several embodiments. In other embodiments, a chisel point is defined.
The drill body for use in association with the roof bit blade insert of the present invention defines an upper end and a lower end. The upper end is configured to receive a blade of the present invention. A transverse slot for mounting the blade has opposing parallel faces, the planes of which are parallel to the longitudinal axis of the body. The faces of the slot are separated by a distance slightly greater than the thickness of the blade. Generally, the transverse slot of the drill body is configured to loosely receive the blade such that it is centered therein. The blade is then brazed to the body in order to be deployed in the field.
For those blades defining a centered protrusion, each of the faces of the slot defines a centered longitudinal recess having an arcuate surface. For those blade embodiments defining trailing end protrusions, each face of the slot is adapted to define a complimentary recess. For those blade embodiments having leading end protrusions defined by either a butterfly taper or a half-butterfly taper, each face of the slot defines a complimentary taper.